Metal's signature sound is the double bass — two bass drum pedals (or one with a double-pedal mechanism) playing rapid alternating kicks. The notation below uses a single bass drum line; in practice, alternate R L R L with your feet, the same way your hands alternate in a single-stroke roll.
The progression: kicks on every quarter (one foot at a time, easy), then 8ths (alternating feet, the actual double-bass technique), then 16ths (the metal staple), then a basic metal groove with the kicks underneath.
Exercises
1 — Quarter-Note Kicks
Single foot, kick on every quarter. This is the warmup — your dominant foot should be able to do this for two minutes without the leg getting tired. If it can't, slow down or work on heel-up technique before adding the second foot.
2 — Eighth-Note Kicks (Alternating Feet)
Eight kicks per bar — now the second foot enters. Alternate R L R L R L R L. The non-dominant foot will feel weaker for the first few hundred reps; that's expected. Focus on even volume between feet, not speed.
3 — Sixteenth-Note Kicks
Sixteen kicks per bar at ♩=80 — sticking R L R L repeated. Tempo dropped slightly because the hand 8ths and foot 16ths together are a real coordination challenge. The hi-hat hand has to stay steady while the feet move twice as fast.
4 — Basic Metal Groove (16th Kicks Underneath)
Basic backbeat in the hands, 16th-note double-bass underneath. This is the core metal sound — the snare on 2 and 4 carries the song while the kicks gallop. Slow it down if needed; this is hard.